One class of rotary blood pump, particularly intended for extracorporeal use, has a shear pump impeller with curved, conical rotating elements. Struts extend radially or axially between the elements to provide structural support. Such pumps are shown in Kletschka U.S. Pat. No. 3,864,055, Rafferty U.S. Pat. No. 3,647,324 and Belanger U.S. Pat. No. 4,507,048. Blood pumps incorporating a conical shear impeller are sold under the Bio-Pump trademark by Bio-Medicus, Minneapolis, Minn. Another form of multi element shear or disc pump is shown in Effenberger U.S. Pat. No. 4,402,647.
The single stage pumps of the prior art have limited capacity. When operated at high rotary speeds, the intraelement struts cause turbulence.